From c34fd0b06c4daee1d0aaf7a1efb7aa7e1fc2fc04 Mon Sep 17 00:00:00 2001
From: Alexander Kuzmenkov <36882414+akuzm@users.noreply.github.com>
Date: Mon, 6 Nov 2023 12:33:07 +0100
Subject: [PATCH] Do not use partial indexes for compression

They refer only to a subset of the table.
---
 .unreleased/fix_partial_index               |  1 +
 tsl/src/compression/compression.c           | 11 ++++++
 tsl/test/expected/compression_indexscan.out | 37 +++++++++++++++++++++
 tsl/test/sql/compression_indexscan.sql      | 10 +++++-
 4 files changed, 58 insertions(+), 1 deletion(-)
 create mode 100644 .unreleased/fix_partial_index

diff --git a/.unreleased/fix_partial_index b/.unreleased/fix_partial_index
new file mode 100644
index 00000000000..5cb091f3338
--- /dev/null
+++ b/.unreleased/fix_partial_index
@@ -0,0 +1 @@
+Fixes: #6280 Potential data loss when compressing a table with a partial index that matches compression order.
diff --git a/tsl/src/compression/compression.c b/tsl/src/compression/compression.c
index d7c916cec23..0b7b8dd1a87 100644
--- a/tsl/src/compression/compression.c
+++ b/tsl/src/compression/compression.c
@@ -291,6 +291,17 @@ compress_chunk(Oid in_table, Oid out_table, const ColumnCompressionInfo **column
 			Oid index_oid = lfirst_oid(lc);
 			Relation index_rel = index_open(index_oid, AccessShareLock);
 			IndexInfo *index_info = BuildIndexInfo(index_rel);
+
+			if (index_info->ii_Predicate != 0)
+			{
+				/*
+				 * Can't use partial indexes for compression because they refer
+				 * only to a subset of all rows.
+				 */
+				index_close(index_rel, AccessShareLock);
+				continue;
+			}
+
 			int previous_direction = NoMovementScanDirection;
 			int current_direction = NoMovementScanDirection;
 
diff --git a/tsl/test/expected/compression_indexscan.out b/tsl/test/expected/compression_indexscan.out
index 6afc209e239..c259f64e22a 100644
--- a/tsl/test/expected/compression_indexscan.out
+++ b/tsl/test/expected/compression_indexscan.out
@@ -912,6 +912,43 @@ SELECT decompress_chunk(show_chunks('tab1'));
 (4 rows)
 
 DROP INDEX idx_asc_null_first;
+-- Can't use partial indexes for compression because they refer only to a subset of the table.
+create index predicate on tab1(id, c1, time nulls first) where c2 = 0;
+select count(*) from tab1;
+ count 
+-------
+ 62400
+(1 row)
+
+select compress_chunk(show_chunks('tab1'));
+INFO:  compress_chunk_tuplesort_start
+INFO:  compress_chunk_tuplesort_start
+INFO:  compress_chunk_tuplesort_start
+INFO:  compress_chunk_tuplesort_start
+             compress_chunk             
+----------------------------------------
+ _timescaledb_internal._hyper_1_1_chunk
+ _timescaledb_internal._hyper_1_2_chunk
+ _timescaledb_internal._hyper_1_3_chunk
+ _timescaledb_internal._hyper_1_4_chunk
+(4 rows)
+
+select decompress_chunk(show_chunks('tab1'));
+            decompress_chunk            
+----------------------------------------
+ _timescaledb_internal._hyper_1_1_chunk
+ _timescaledb_internal._hyper_1_2_chunk
+ _timescaledb_internal._hyper_1_3_chunk
+ _timescaledb_internal._hyper_1_4_chunk
+(4 rows)
+
+select count(*) from tab1;
+ count 
+-------
+ 62400
+(1 row)
+
+drop index predicate;
 --Tear down
 DROP TABLE tab1;
 DROP TABLE tab2;
diff --git a/tsl/test/sql/compression_indexscan.sql b/tsl/test/sql/compression_indexscan.sql
index f9a8cb93e03..cf23a3b525c 100644
--- a/tsl/test/sql/compression_indexscan.sql
+++ b/tsl/test/sql/compression_indexscan.sql
@@ -251,8 +251,16 @@ SELECT compress_chunk(show_chunks('tab1'));
 SELECT decompress_chunk(show_chunks('tab1'));
 DROP INDEX idx_asc_null_first;
 
+-- Can't use partial indexes for compression because they refer only to a subset of the table.
+create index predicate on tab1(id, c1, time nulls first) where c2 = 0;
+select count(*) from tab1;
+select compress_chunk(show_chunks('tab1'));
+select decompress_chunk(show_chunks('tab1'));
+select count(*) from tab1;
+drop index predicate;
+
 --Tear down
 DROP TABLE tab1;
 DROP TABLE tab2;
 DROP TABLE tab3;
-SET timescaledb.show_compression_path_info = 'off';
\ No newline at end of file
+SET timescaledb.show_compression_path_info = 'off';